Semiconductor manufacturing processes operate on a very small scale, where the tiniest amount of impurity in a semiconductor wafer can render the device inoperable. For this reason, there is a need for improved manufacturing methods that can help reduce the appearance and effects of impurities. Some such methods involve highly-filtered clean rooms, to help ensure that unwanted particulates are removed from the interior environment. While such filtering systems are beneficial, they are far from perfect, and there remain various types of impurities that can still exist in the filtered clean room. When such impurities remain in the clean room, they may unfortunately be absorbed by the semiconductor wafers and devices during the manufacturing process, leading to undesired results.
FIG. 1 illustrates a basic example of a semiconductor device during a manufacturing process that may experience such undesired results. In the process, circuit components are formed on a substrate, such as an interlayer (or interlevel) dielectric (ILD) 100. Components are formed by creating trenches 101 in the ILD 100, where the trenches are filled with different conductive/insulating/semiconductive materials to form interconnections, transistor elements, etc. of a semiconductor circuit. When the ILD 100 is manufactured in an environment having impurities, such as water moisture and ammonia particles, those impurities may be absorbed by the ILD 100. The absorption of such particles into the ILD 100 may have the undesired effect of lowering the dielectric constant (k) of the device(s) created on the ILD 100.
Manufacturing processes may include some steps, such as annealing, that may allow the ILD 100 to outgas some of the absorbed impurities. However, this outgassing might not occur uniformly. For example, ILD 100 may include some portions 102 that are relatively densely populated with trenches, while other portions 103 are more isolated, and not as densely populated. These portions experience different amounts of outgassing. In the denser portion 102, more outgassing can occur because of the larger surface area of the ILD 100 exposed by the trenches (e.g., the side walls of the trenches that extend into the ILD 100, and create additional surface area). In the less dense portion 103, less outgassing can occur because there is a smaller exposed surface area due to there being fewer trenches.
This imbalance in outgassing can lead to a variation in the ILD 100's dielectric constant (k) across portions of the device. Such variation can make it more difficult to reliably design and construct semiconductor devices, and it would be an advance in the art if this imbalance could be reduced and/or minimized.